Creep Resistant and Reprocessable Polyamide Networks Based on Reversible Lactone Ring-Opening

Amides are robust chemical linkages of interest in the field of dynamic covalent polymer networks (DCPNs), but their activation towards dynamic exchange remains an outstanding challenge. Herein, we introduce γ-hydroxy amides as a versatile motif for the design of creep resistant, yet fully reprocessable crosslinked polyamide-based materials. This was achieved by the reversible ring-opening of γ-lactones with primary amines. Small molecule kinetic studies showed that temperatures exceeding 120 °C are required for the ring-closure to occur at a significant rate. Thus, efficient exchange of the γ-hydroxy amide bonds was expected upon heating, while essentially non-dynamic covalent amide bonds should prevail at lower temperatures. γ-Hydroxy amides were then introduced into DCPNs, for which a newly prepared bifunctional γ-lactone monomer was cured with amine hardeners. A marked thermal response was observed in the rheological behavior, while creep resistance comparable to that of a non-dynamic epoxy-amine network was maintained up to 120 °C. Finally, we could also demonstrate the thermal resilience of γ-hydroxy amides after multiple compression molding cycles for a material with a glass transition temperature above 80 °C. Consequently, we expect that this simple chemistry platform has high potential for application in reprocessable thermoset materials.